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Lecture

APLUS PSYA01 Textbook Notes - Chap 5-9.pdf


Department
Psychology
Course Code
PSYA01H3
Professor
Steve Joordens

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Notes by Mary Lee Notes from Psychology the Science of Behavior 4th Ed Carlson/Heth
CHAPTER 5: Sensation
- Everything we learn is detected by sense organs and transmitted to our brains by sensory nerves
- Sense organs and sensory nerves provide us with useful information about the outside world
- But how specific that information is depends on things like: the specific modality of the information, the
characteristics of the information, the state of the brain at the time it receives it
- information from different sources in the environment are processed differently by sensory systems
- Ex. there is a clear difference between vision and audition
- Vision: we see different things every second, but we have a sense that our visual world is stable
- the visual system must provide that stability
- Sound: it is not so variable the intensity of sound changes depending on how far we are from the source, but these
changes are more gradual than those faced by the visual system
- also, sounds can go around obstacles, unlike light
- our auditory sense has more time to process signals
- So our senses are attuned to different aspects of our world, and they combine together to give us a rich experience of
the world
- Audition is important for social behavior, vision for information about distant events, sense of smell can tell us about
sources of aromatic molecules far upwind
- Taste and touch deal with events occurring immediately nearby
Sensory Processing
- Experience is traditionally studied by distinguishing between sensation and perception
- Sensation: the detection of the elementary properties of a stimulus
ex. seeing the colour red, seeing a movement
- Perception: the detection of the more complex properties of a stimulus, including its location and nature; involves
learning
ex. seeing a red apple, seeing a soccer ball coming and realizing you need to move to block it
- Detecting a sound is not the same as identifying what the source of the sound means
- Long ago, they thought that perceptions depended on learning, and sensations involved innate, prewired physiological
mechanisms
- But until now, there has been no clear boundary between “simple” sensations and “complex” perceptions
- Research: experience is essential to the development of some of the most elementary features of sensory systems
- We will look at our sensory mechanisms: the visual, auditory, gustatory, olfactory, somatosensory systems
- Tradition 5 senses; but we actually have several more
- Ex. the somatosensory system can be separated into various components for: touch, warmth, coolness, vibration,
physical damage, head tilt, etc.
- it just depends if you want to use the term “sense” for them
Transduction
- The brain is separated from the outside world and the only receptors it has looks at temperature and salt concentration
of the blood no receptors for the outside world
- Useful actions require information from the external world, so this information is gathered by the sense organs located
outside of the brain

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Notes by Mary Lee Notes from Psychology the Science of Behavior 4th Ed Carlson/Heth
- Sense organs detect stimuli (from light, sound, odor, taste, mechanical contact) from the environment transported
to brain through neural impulses
- it is the task of the sense organs to transmit signals to the brain that are coded to represent events in the environment
- the brain analyzes this information and reconstructs what just happened
- Transduction: the conversion of physical stimuli into changes in the activity of receptor cells of sensory organs
- energy from environmental events neural activity
- each sense organ responds to a particular form of energy and translates it into neural firing
- The means of transduction for most cases is specialized neurons called receptor cells
receptor cell: a neuron that directly responds to a physical stimulus, such as light, vibrations, or aromatic molecules
- they release chemical transmitter substances that stimulate other neurons, thus altering the rate of firing of their
axons
- For the somatosensory systems, dendrites of neurons respond directly to physical stimuli without the intervention of
specialized receptor cells
- but there may still be a bit of specialization: some of these neurons have specialized endings that let them respond to
particular kinds of sensory information
The Types of Transduction Accomplished by the Sense Organs
Location of Sense Organ
Environmental Stimuli
Energy Transduced
Eye
Light
Radiant energy
Ear
Sound
Mechanical energy
Vestibular system
Tilt and rotation of head
Mechanical energy
Tongue
Taste
Recognition of molecular shape
Nose
Odour
Recognition of molecular shape
Skin, internal organs
Touch
Temperature
Vibration
Mechanical energy
Thermal energy
Mechanical energy
Muscle
Pain
Stretch
Chemical reaction
mechanical energy
Sensory Coding
- Sensory information is translated into firing of action potentials, but there aren’t different types of action potentials
- But we can still detect a lot of different stimuli with each of our sense organs
ex. we can discriminate among 7.5 million different colours, we can recognize up to 10 000 odors
- discriminate the degree of pressure involved, sharpness or bluntness, softness or hardness, and temperature of the
object we’re touching
- You may ask, if action potentials can’t be altered, how do the sensory organs tell the brain a red apple or a yellow
lemon that you see, for ex?
- the information must be coded somehow in the activity of the axons, and it is in two general forms: anatomical
coding and temporal coding
Anatomical Coding
- Recall Muller’s doctrine of specific nerve energies the brain learns what is happening through the activity of
specific sets of neurons
- sensory organs are in different places and send their information to the brain through different sets of nerves
- The brain uses anatomical coding to interpret the location and type of sensory stimulus according to which incoming
nerve fibres are active
anatomical coding: a means by which the nervous system represents information; different features are coded by the
activity of different neurons

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Notes by Mary Lee Notes from Psychology the Science of Behavior 4th Ed Carlson/Heth
- Ex. rub your eyes light-sensitive receptors are there, and they are mechanically stimulated action potentials are
produced in the optic nerves brain acts as if the neural activity in the optic nerves was produced by light you see
stars and flashes
- This can be seen in the other senses too
- artificially stimulate the nerves that convey taste sensation of taste
- electrical stimulation of the auditory nerve sensation of a buzzing noise
Temporal Coding
- Temporal coding: a means by which the nervous system represents information; different features are coded by the
pattern of activity of neurons
- it is in terms of time
- The simplest form of temporal code is rate: by firing at a faster/slower rate according to the intensity of a stimulus, an
axon can communicate quantitative information to the brain
- Ex. light touch encoded by a low rate of firing; more forceful touch by a high rate of firing
- Anatomical coding: The firing of particular set of neurons tells where the body is being touched
- Temporal coding: the rate at which these neurons fire tells how intense that touch is
Psychophysics
- Psychophysics: a branch of psychology that measures the quantitative relation between physical stimuli and
perceptual experience
- physics of the mind
- Scientists have to find ways to measure people’s sensations, and there are two methods: the just-noticeable difference
and the procedures of signal detection theory
The Principle of the Just-Noticeable Difference
- Weber looked at the ability of humans to discriminate between various stimuli, he measured the just-noticeable
difference (jnd)
- just-noticeable difference (jnd): the smallest difference between two similar stimuli that can be distinguished; also
called difference threshold
- The jnd is directly related to the magnitude of that stimulus
- Give people two metal objects and ask if they were different in weight
- participants said they were the same unless they differed by a factor of 1 in 40 (they could barely distinguish 40 g
and 41 g; 80 g and 82 g, etc.
- the difference in weight between 40 and 41 g, and 80 and 82 g is the jnd
- Different senses had different ratios
ex. ratio for differences in brightness of white light is 1 in 60
- Weber fraction: the ratio between a jnd and the magnitude of a stimulus; reasonably constant over the middle range
of most stimulus intensities
- Fechner: used Weber’s concept of the jnd to measure people’s sensations
- assumption: the jnd was the basic unit of a sensory experience
- he measured the absolute magnitude of a sensation in jnds
- Experiment: put participant in dark room and have two bulbs (one is sample, one is comparison)
- sample is turned off, comparison is brightened until they notice a difference the value is one jnd
- set sample to one jnd, comparison is brightened until they notice a difference the value is two jnds
- continue this until the lights become uncomfortably bright
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